The larva pupated on day 5; so it was a 4th instar larva the whole time I had it. I didn't take a picture of the prepupa because I didn't want to disturb it. Even the pupa reacts to disturbance - I accidentally touched it while picking up the leaf for this photo, and it began to vigorously snap up and down. The snapping continued through the 5-minute photo session and it was still going, although not as quickly, when I returned it to the container.

I anticipate that the adult beetle will be about the same length as the pupa, 8 mm. It's about half the length that the larva was at its maximum size.